For a long time, the surface treatment capacity of China's manufacturing industry has lagged far behind production, which has greatly limited the process of turning the manufacturing industry from big to strong. With the implementation of the "14th Five Year Plan" strategic plan, the demand for advanced processes, especially high-end manufacturing and energy conservation and emission reduction, is becoming increasingly urgent. In terms of surface treatment, there is an urgent need to comprehensively upgrade the technology and process in China. Traditional cleaning processes, such as mechanical friction cleaning, chemical corrosion cleaning, powerful impact cleaning, and high-frequency ultrasonic cleaning, not only have long cleaning cycles, are difficult to achieve automation, have harmful effects on the environment, and cannot achieve ideal cleaning effects, which cannot well meet the needs of fine processing.

However, with the increasingly prominent contradiction between environmental protection, high efficiency, and high accuracy, its application is facing great challenges. At the same time, various cleaning technologies that are conducive to environmental protection and suitable for parts in the field of ultra precision machining have emerged, and laser cleaning technology is one of them.

Laser cleaning concept

Laser cleaning is a technology that uses focused laser light to act on the surface of a material to rapidly vaporize or peel off surface contaminants, thereby achieving material surface cleaning. Compared to various traditional physical or chemical cleaning methods, laser cleaning has the characteristics of no contact, no consumables, no pollution, high accuracy, no damage or small damage, and is an ideal choice for the new generation of industrial cleaning technology.

Principles of laser cleaning

The principle of laser cleaning is relatively complex, and may include both physical and chemical processes. In many cases, it is mainly physical processes accompanied by partial chemical reactions. The main processes can be summarized into three categories, including gasification processes, shock processes, and oscillation processes.
 

• Gasification process

When a high-energy laser irradiates the surface of a material, the surface absorbs laser energy and converts it into internal energy, rapidly increasing the surface temperature to above the material's vaporization temperature, thereby causing contaminants to escape from the material surface in the form of steam. Selective vaporization usually occurs when the absorption rate of surface contaminants to laser light is significantly higher than the absorption rate of base materials to laser beam. A typical application case is the cleaning of dirt on stone surfaces. As shown in the figure below, the pollutants on the stone surface have a strong absorption of laser light and are rapidly vaporized. When contaminants are removed and laser light is irradiated on the stone surface, the absorption is weak, and more laser energy is scattered by the stone surface. As a result, the temperature change on the stone surface is small, and the stone surface is protected from damage.
 

• Impact process

The shock process is a series of reactions that occur during the interaction between laser and material, resulting in the formation of shock waves on the surface of the material. Under the action of shock waves, surface contaminants break up and become dust or debris that peel off from the surface. There are various mechanisms that cause shock waves, including plasma, steam, and rapid thermal expansion and contraction. Under the action of shock waves, surface contaminants break up and become tiny dust, particles, or debris. When the laser is moved away from the irradiation position, the plasma disappears immediately, creating a local negative pressure, and particles or debris of pollutants are removed from the surface.
 

• Oscillating process

Under the action of short pulses, the process of temperature rise and temperature decrease of materials is extremely rapid. Due to the different thermal expansion coefficients of different materials, surface contaminants and the substrate will undergo high-frequency and varying degrees of thermal expansion and contraction under short pulse laser irradiation, resulting in oscillatory effects that cause contaminants to peel off from the surface of the material. During this peeling process, vaporization of the material may not occur, nor may plasma be generated. Instead, the shear force formed at the interface between the pollutant and the substrate under the action of oscillation destroys the bond between the pollutant and the substrate. Research has shown that when the incident angle of the laser is slightly increased, it can increase the contact between the laser and the particle pollutants and the substrate interface, reduce the threshold value of laser cleaning, make the oscillation effect more obvious, and improve the cleaning efficiency.

Industrial Application of Laser Cleaning Machine

1. Mold industry

Laser can achieve non-contact cleaning of molds, which is very safe for the mold surface, ensuring its accuracy, and can clean submicron scale dirt particles that cannot be removed by traditional cleaning methods, achieving true pollution-free, efficient, and high-quality cleaning.

2. Precision instrument industry

The precision machinery industry often requires the removal of esters and mineral oils used for lubrication and corrosion resistance from parts, usually by chemical methods, but chemical cleaning often still has residues. Laser ester removal can completely remove esters and mineral oils without damaging the surface of parts. Laser induced explosive vaporization of a thin layer of oxide on the surface of a part creates a shock wave that leads to dirt removal rather than mechanical interaction.

3. Rail industry

Currently, all rail pre welding cleaning uses grinding wheels and abrasive belts, resulting in severe damage to the base material and severe residual stress. In addition, a large amount of grinding wheel consumables are consumed every year, resulting in high costs and serious dust pollution to the environment. Laser cleaning can provide high-quality and efficient green cleaning technology for the production of high-speed railway track laying in China, solve the above problems, eliminate welding defects such as seamless rail holes and gray spots, and improve the stability and safety of high-speed railway operation in China.

4. Aviation industry

The surface of an aircraft needs to be repainted after a certain period of time, but the original old paint needs to be completely removed before painting. Chemical soaking/wiping is the main paint removal method in the aviation field. This method causes a large amount of chemical auxiliary waste, and it is also unable to achieve local maintenance paint removal. This process is heavy and harmful to health. Laser cleaning can achieve high-quality removal of paint from aircraft skin surfaces, and is easy to achieve automated production. Currently, this technology has been applied to the maintenance of some high-end models abroad.

5. Shipbuilding industry

Currently, the main method of ship pre production cleaning is sand blasting, which has caused serious dust pollution to the surrounding environment and has gradually been banned, resulting in reduced production or even shutdown of ship production enterprises. Laser cleaning technology will provide a green and pollution-free cleaning solution for anti-corrosion coating of ship surfaces.

Nowadays, advanced manufacturing has become the commanding height of international competition, and laser manufacturing is a key task deployed during the "13th Five Year Plan" period in China. As an advanced technology in laser manufacturing, laser cleaning technology has great potential for application in industrial development. Vigorously developing laser cleaning technology is of great strategic significance for the significant improvement of international competitiveness of high-end laser manufacturing technology and equipment, as well as economic and social development.

About HGTECH: HGTECH is the pioneer and leader of laser industrial application in China, and the authoritative provider of global laser processing solutions. We have comprehensively arranged laser intelligent machine, measurement and automation production lines, and smart factory construction to provide overall solutions for intelligent manufacturing.